1. Field of the Invention
The invention relates to a hybrid vehicle that includes an engine and a motor that generate drive power for driving the hybrid vehicle, and a method of controlling the hybrid vehicle.
2. Description of the Related Art
In a hybrid vehicle, importance is placed on fuel efficiency. Therefore, the ratio between drive power generated by an engine and drive power generated by a motor needs to be changed, or a travel mode needs to be switched between a hybrid vehicle travel mode and an electric vehicle travel mode, in order to efficiently consume available electricity in a battery. Particularly in a plug-in hybrid vehicle in which a battery is charged with electricity supplied from an external power source (for example, a power source for domestic use), it is preferable that the available electricity in the battery should be used up when the hybrid vehicle reaches a destination (i.e., a point at which the battery can be charged). In a hybrid vehicle described in Japanese Patent Application Publication No. 2008-87719 (JP-A-2008-87719), a coordinated control is executed using a navigation system. Required amount of electricity is determined based on map data (for example, a gradient) relating to a route to the destination, and the amount of electricity to be consumed is estimated. Thus, a travel mode is switched between a hybrid vehicle travel mode and an electric vehicle travel mode so that available electricity in a battery is consumed as much as possible until the hybrid vehicle reaches the destination.
In the above-described hybrid vehicle, the travel mode is switched between the hybrid vehicle travel mode and the electric vehicle travel mode based on gradient information in the map data. Therefore, the travel mode may be switched between the hybrid vehicle travel mode and the electric vehicle travel mode at a point different from an actual gradient change point at which the actual gradient changes, depending on accuracy of the gradient change point in the map data, and accuracy of detecting a current position of the vehicle. In this case, drive power changes due to the switching of the travel mode between the hybrid vehicle travel mode and the electric vehicle travel mode, when the hybrid vehicle is not located at the actual gradient change point. Accordingly, an occupant feels discomfort. For example, in the case where a flat road leads to a steep upward gradient, if the travel mode is switched from the electric vehicle travel mode to the hybrid vehicle travel mode before the hybrid vehicle reaches the actual gradient change point, the occupant feels discomfort due to an increase in the drive power, and if the travel mode is switched from the electric vehicle travel mode to the hybrid vehicle travel mode after the hybrid vehicle passes the actual gradient change point, the occupant feels discomfort due to insufficiency of the drive power.